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   * Copyright 2010 JBoss Inc
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
 package org.drools.runtime;
StatelessKnowledgeSession provides a convenience API, wrapping StatefulKnowledgeSession. It avoids the need to call dispose(). Stateless sessions do not support iterative invocations, the act of calling execute(...) is a single shot method that will internally instantiate a StatefulKnowledgeSession, add all the user data and execute user commands, call fireAllRules, and then call dispose(). While the main way to work with this class is via the BatchExecution Command as supported by the CommandExecutor interface, two convenience methods are provided for when simple object insertion is all that's required.

Simple example showing a stateless session executing for a given collection of java objects using the convenience api. It will iterate the collection inserting each element in turn

 KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
 kbuilder.add( ResourceFactory.newFileSystemResource( fileName ), ResourceType.DRL );
 assertFalse( kbuilder.hasErrors() );
 if (kbuilder.hasErrors() ) {
     System.out.println( kbuilder.getErrors() );
 KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
 kbase.addKnowledgePackages( kbuilder.getKnowledgePackages() );
 StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();
 ksession.execute( collection );

If this was done as a single Command it would be as follows:

 ksession.execute( CommandFactory.newInsertElements( collection ) );

Note if you wanted to insert the collection itself, and not the iterate and insert the elements, then CommandFactory.newInsert( collection ) would do the job.

The CommandFactory details the supported commands, all of which can be marshalled using XStream and the BatchExecutionHelper. BatchExecutionHelper provides details on the XML format as well as how to use Drools Pipeline to automate the marshalling of BatchExecution and ExecutionResults.

StatelessKnowledgeSessions support globals, scoped in a number of ways. I'll cover the non-command way first, as commands are scoped to a specific execution call. Globals can be resolved in three ways. The StatelessKnowledgeSession supports getGlobals(), which returns a Globals instance. These globals are shared for ALL execution calls, so be especially careful of mutable globals in these cases - as often execution calls can be executing simultaneously in different threads. Globals also supports a delegate, which adds a second way of resolving globals. Calling of setGlobal(String, Object) will actually be set on an internal Collection, identifiers in this internal Collection will have priority over supplied delegate, if one is added. If an identifier cannot be found in the internal Collection, it will then check the delegate Globals, if one has been set.

Code snippet for setting a session scoped global:

 StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();
 ksession.setGlobal( "hbnSession", hibernateSession ); // sets a global hibernate session, that can be used for DB interactions in the rules.
 ksession.execute( collection ); // this will now execute and will be able to resolve the "hbnSession" identifier.

The third way is execution scopped globals using the CommandExecutor and SetGlobal Commands:

 List<Command> cmds = new ArrayList<Command>();
 cmds.add( CommandFactory.newSetGlobal( "list1", new ArrayList() ) );
 cmds.add( CommandFactory.newInsert( new Person( "jon", 102 ) ) );
 ksession.execute( CommandFactory.newBatchExecution( cmds ) );

The CommandExecutor interface also supports the ability to export data via "out" parameters. Inserted facts, globals and query results can all be returned.

 List<Command> cmds = new ArrayList<Command>();
 cmds.add( CommandFactory.newSetGlobal( "list1", new ArrayList(), true ) );
 cmds.add( CommandFactory.newInsert( new Person( "jon", 102 ), "person" ) );
 cmds.add( CommandFactory.newQuery( "Get People" "getPeople" );
 ExecutionResults results = ksession.execute( CommandFactory.newBatchExecution( cmds ) );
 results.getValue( "list1" ); // returns the ArrayList
 results.getValue( "person" ); // returns the inserted fact Person
 results.getValue( "Get People" );// returns the query as a QueryResults instance.

See also:
public interface StatelessKnowledgeSession
Return the Globals store
    Globals getGlobals();

Sets a global value on the globals store

identifer the global identifier
value the value assigned to the global identifier
    void setGlobal(String identifer,
                   Object value);
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